1. Field of the Invention
The present invention is directed to lightweight but extremely high power low frequency transducers that are capable of operating at continuous power levels in a range of 3000 watts. To permit operation at such high power levels, the transducers of the invention are provided with an advanced heat sink construction and an air ventilating system that maximizes heat dissipation from the voice coils of the transducers.
2. Brief Description of the Related Art
A primary problem with large low frequency audio speakers or transducers is that as power is increased, there is an accompanying increase in the build up of heat in the voice coil. A large portion of the input power into a speaker or transducer is converted into heat within the coil. As electrical energy is supplied to the coil, the coil temperature rises. With the increase in coil temperature there is an increase in DC resistance within the coil which results in a loss of operating power. This heating is referred to as power compression, wherein a portion of the input power is effectively being turned into heat energy rather than sound energy. Not only can the long term power handling of the transducer suffer, but there is a mechanical limitation as well. The adhesives used to assemble the voice coil and coil cylinder will reach a melting point and the coil will eventually break apart and the system will fail.
In order to move a lot of air in an audio speaker or transducer, it is necessary to increase the size, that is the diameter, of the driver or speaker cone and/or increase the excursion or movement of the cone. However, with large drivers, as the diameter of the cone increases the cone becomes heavier and less rigid, thereby decreasing the efficiency and the transient response. Also, the larger the cone, the more power that is needed to move it and the greater the heat energy that is developed. Further, any perturbation in the geometry of a cone as it is forced through the air by the coil results is distortion and lowers the power handling capability of the driver. For these reasons, the diameter of most drivers has been conventionally limited to 18 inches or less, especially for paper cones. At larger sizes, a difference of one inch in diameter makes a significant difference in the mass necessary to maintain the required stiffness in a cone.
An additional problem for the larger drivers that have a greater throw or movement is that as the cone moves through its excursion, it often encounters uneven forces caused by a shape of the transducer box or housing or a room wherein the box or housing is placed. The cone then transfers the non axis-symmetric energy to the coil causing it to shift in a surrounding air gap, a phenomenon known as “cone rocking”. To overcome this, most systems are developed with wider air gaps. Although this increase in tolerance of the air gap permits some “cone rocking” without adversely effecting the sound output, the wider gap not only requires more powerful magnets to maintain flux density across the additional gap space, but also results in a greater volume of air which functions as an insulator in the gap. Thus, the greater the air gap, the greater the build up of heat within the transducer with a resulting loss of operating power.
In an average conventional driver, the piston, which is the coil and the cone, is supported in two places, normally at a surround and at a spider. These two elements maintain the coil centered in the air gap and are generally sufficient axial support for drivers with short throw excursions and the “cone rocking” is usually not a problem, however, the larger drivers with greater excursions, greater support is necessary.